1. Field of the Invention
The present invention relates to a control apparatus for continuously variable transmission for use with a vehicle which can continuously vary the output of an internal combustion engine.
2. Description of the Prior Art
A conventional control apparatus for a continuously variable transmission of the type mentioned above is known, for example, from Japanese Patent No. 3,218,962. This continuously variable transmission is applied to an internal combustion engine equipped in a vehicle. The control apparatus provides an automatic transmission mode and a manual mode for the continuously variable transmission. In the automatic transmission mode, the transmission is controlled to continuously change the transmission ratio thereof to a target transmission ratio which is continuously set in accordance with a vehicle speed and the like. In the manual mode, on the other hand, one of a plurality of transmission stages is selected in accordance with an operation performed by a driver on a shift lever, and a target transmission ratio is set to a predetermined transmission ratio corresponding to the selected transmission ratio. The transmission ratio of the continuously variable transmission is controlled to reach the target transmission ratio which is set as mentioned. These two transmission modes are switched from one to the other during an operation of the engine by an operation performed by the driver on the shift lever. Particularly, a switching operation from the automatic transmission mode to the manual mode is performed in the following manner. First, an actual transmission ratio at the time of the switching is compared with a target transmission ratio of each transmission stage. A transmission stage immediately after the switching is shifted to the High-side transmission stage closest to the transmission ratio in a first implementation, and to the closest Low-side transmission stage in a second implementation. The latter case is equivalent to shifting down the transmission stage, which can be utilized as a brake. In the former case, each time the driver operates the shift lever to the High side or to the Low side, the transmission is shifted up or down by one stage.
According to the conventional control apparatus for a continuously variable transmission described above, after the automatic transmission mode is switched to the manual mode, the transmission is fixed at a preset High-side or Low-side predetermined transmission stage, i.e., a constant transmission ratio irrespective of a particular operating condition of the engine until the driver operates the shift lever. For this reason, if the driver performs the aforementioned switching and shifts the transmission to the High side in a situation where the vehicle is climbing up a slope and therefore requires a high engine torque, the engine torque can be insufficient. Also, if the aforementioned switching is caused by an erroneous operation, the driver is often unaware that the continuously variable transmission has been switched to the manual mode because the transmission ratio of the continuously variable transmission is fixed at a constant transmission ratio. Therefore, for example, if the driver keeps treading down the accelerator pedal for acceleration without being aware that the transmission has been shifted to the Low side upon switching, the engine would be burdened with possible over-revolution.
The present invention has been made to solve the problem mentioned above, and it is an object of the invention to provide a control apparatus for a continuously variable transmission which is capable of permitting a driver to select one from three transmission modes for the continuously variable transmission, and providing an appropriate transmission ratio in accordance with a particular operating condition of a vehicle without causing an insufficient engine torque or over-revolution, particularly when the transmission is switched from a continuously variable transmission mode to a stepped manual transmission mode.
To achieve the above object, the present invention provides a control apparatus for a continuously variable transmission for use with a vehicle, capable of continuously varying the output of an internal combustion engine. The control apparatus is characterized by comprising operating condition detecting means for detecting an operating condition of the vehicle; continuous automatic transmission mode executing means for executing a continuous automatic transmission mode for continuously setting a transmission ratio of the continuously variable transmission in accordance with the detected operating condition of the vehicle as a transmission mode for the continuously variable transmission; stepped automatic transmission mode executing means for executing a stepped automatic transmission mode for setting the transmission ratio of the continuously variable transmission to one of a plurality of predetermined transmission stages in accordance with the detected operating condition of the vehicle as the transmission mode for the continuously variable transmission; stepped manual transmission mode executing means for executing a stepped manual transmission mode for setting the transmission ratio to one of a plurality of predetermined transmission stages in accordance with a driver""s intention of transmission as the transmission mode for the continuously variable transmission; switch operating means manipulated for switching the transmission mode of the continuously variable transmission; and transmission mode setting means for setting the continuously variable transmission to one of the continuous automatic transmission mode, the stepped automatic transmission mode and the stepped manual transmission mode in accordance with a manipulating state of the switch operating means.
According to this control apparatus for a continuously variable transmission for use with a vehicle, the stepped automatic transmission mode is provided as a transmission mode for the continuously variable transmission in addition to the continuous automatic transmission and stepped manual transmission. The continuously variable transmission is set to one of the three transmission modes in accordance with a manipulating state of the switch operating means. When the continuously variable transmission is set to the stepped manual transmission mode, the transmission ratio can be provided step by step in accordance with the driver""s intention of transmission. Also, when the continuously variable transmission is set to the continuous automatic transmission mode or stepped automatic transmission mode, an appropriate transmission ratio can be provided in a continuous manner or step by step in accordance with a particular operating condition of the vehicle.
Preferably, in the control apparatus for a continuously variable transmission for use with a vehicle described above, the transmission mode setting means temporarily sets the continuously variable transmission to the stepped automatic transmission mode when the switch operating means is manipulated to switch from the continuous automatic transmission mode to the stepped manual transmission mode.
According to this preferred embodiment of the control apparatus, when the switch operating means is manipulated to switch the continuously variable transmission from the continuous automatic transmission mode to the stepped manual transmission mode, the continuously variable transmission is not immediately switched from the continuously variable transmission mode to the stepped manual transmission mode, but is temporarily set to the stepped automatic transmission mode. As a result, the continuously variable transmission is not fixed at a constant transmission ratio, but is set to an appropriate transmission stage at all times in accordance with a particular operating condition of the vehicle, thereby making it possible to ensure a proper engine torque when the continuously variable transmission is switched from the continuous automatic transmission mode to the stepped manual transmission mode. Also, in the present invention, even when the driver erroneously operates the switch operating means to switch the continuously variable transmission, for example, from the continuous automatic transmission mode to the stepped manual transmission mode, the continuously variable transmission is temporarily set to the stepped automatic transmission mode, so that the transmission ratio is changed step by step in accordance with a particular operating condition of the vehicle. In this way, the driver can feel the change in the transmission mode, thereby preventing over-revolution and the like.
Preferably, the control apparatus for a continuously variable transmission for use with a vehicle further comprises transmission stage changing means manipulated for changing the continuously variable transmission from one transmission stage to another, wherein the transmission mode setting means sets the continuously variable transmission to the stepped manual transmission mode when the transmission stage changing means is manipulated after the continuously variable transmission has been temporarily set in the stepped automatic transmission mode.
According to this preferred embodiment of the control apparatus, when the transmission stage changing means is manipulated after the continuously variable transmission has been temporarily set in the stepped automatic transmission mode, the continuously variable transmission is switched to the stepped manual transmission mode. Thus, the continuously variable transmission is switched to the stepped manual transmission mode after confirming the driver""s intention of transmission whether he really wishes to change the transmission stage, so that the continuously variable transmission can be appropriately switched to the stepped manual transmission mode while avoiding a switching which would be otherwise made due to an erroneous manipulation on the switch operating means.